The present invention relates to a degassing system for a hydrocarbon dispenser.
In hydrocarbon dispensers, it is known that it is necessary to degas the hydrocarbon in order to ensure that the volume of hydrocarbon delivered to a user does indeed correspond to hydrocarbon and not to a volume mixture of liquid hydrocarbon plus gas.
In European patent No. 0 357 513, a hydrocarbon dispenser is described that includes means for monitoring the gas content of the hydrocarbon. In that document, the hydrocarbon dispenser is provided with a vortex type degasser which is associated with detection means enabling hydrocarbon dispensing to be interrupted as soon as the gas content therein exceeds a predetermined value. Vortex degassers are commonly used in that type of installation. They consist in establishing a helical flow of liquid-and-gas mixture in an elongate cylindrical enclosure, in taking off the liquid-enriched fraction via a lateral tube, and in taking off a gas-enriched fraction via an axial tube.
Accompanying FIG. 1 is a diagram showing a degassing device as commonly used in hydrocarbon dispensers. In this figure, a pump 12 is shown causing hydrocarbon to pass from a storage tank 14 to a vortex degasser 16 which is constituted by an elongate cylindrical enclosure, as mentioned above. The hydrocarbon, possibly containing gas, is injected to a first end of the enclosure 16 by duct 18 in such a manner as to establish helical motion of the hydrocarbon inside the enclosure 16. Degassed hydrocarbon is taken via lateral duct 22 while a liquid fraction that is possibly enriched in gas is taken via axial duct 20. Exit tube 20 is connected to a duct 26 which is in turn connected to a degassing tank or vessel 24.
Looking at the device of FIG. 1, it will be understood that one of the problems associated with such a system is that in the most usual situation of the gas content being very low, the axial takeoff tube 20 is in fact going to take off a non-negligible quantity of hydrocarbon, possibly containing very little gas. It will be understood that this hydrocarbon which is transferred to the degassing vessel reduces the effective efficiency of the installation since this hydrocarbon fraction must be recycled to the inlet of the pump 12 after spending a length of time in the vessel 24.
In contrast, it will be understood that when, accidentally, the hydrocarbon happens to have a high gas content, it is necessary to provide a takeoff tube 20 of diameter that is sufficient to take off effectively the entire gas-filled hydrocarbon fraction.
Also known, from U.S. Pat. No. 2,779,503, is a degassing system of the type shown in FIG. 1, in which the end of the duct opening out in the degassing vessel carries a non-return valve of effective through section that is adjustable by the action of a float resting on the liquid contained in the vessel. When the liquid content is large in the liquid/gas mixture taken off at the outlet from the degassing enclosure, the vessel fills with liquid, thus having the effect of raising the level of the liquid in the degassing vessel, and thus closing the section of the valve. Conversely, if the mixture taken off is rich in gas, then the level of liquid in the vessel remains substantially constant and the valve remains open to pass gas.
However, it can be observed that the above-known degassing system has a response time that is relatively long since when the liquid/gas mixture becomes enriched in liquid it is necessary to allow enough liquid to pour pointlessly into the degassing vessel to cause the liquid level to rise far enough to cause the valve to move through its entire stroke from its open position to its closed position.